Interest in power over ethernet technology has increased with the adoption of the power over ethernet IEEE 802.3af standard in June of 2003. Generally, power over ethernet technology allows standard ethernet cables to carry not only data signals, but also power to the devices connected to the cables. In this manner, power can be provided by the ethernet cable itself, rather than requiring a separate source of power for the connected devices.
The standard requires a power sourcing unit, which supplies up to 15.4 watts of power (at 48 volts) to a powered device. The standard utilizes pins 1/2 and 3/6, or pins 4/5 and 7/8, of the eight-pin ethernet cable for both data and power transfer. To avoid damaging non-compliant devices that may be connected to the power over ethernet system, the standard specifies a method for detecting compliant devices by applying a small, current-limited voltage to check for the presence of a 25 k ohm impedance in the connected device. Only if the power sourcing unit detects this impedance is the full 48 volts applied.
There are many potential applications for power over ethernet technology. For example, wireless access points can be placed at desired locations throughout a building without requiring a separate source of power. Another potential application includes internet protocol (IP) telephones, for which a central power supply with a backup uninterrupted power supply (UPS) is desirable. Other applications for which this technology may be desirable include IP cameras, security badge readers, etc.
The advantages associated with power over ethernet technology can include: reduced cabling costs, because both power and data are provided over a single ethernet cable; increased reliability, because a centralized power source can utilize an UPS to guarantee uninterrupted power to all powered devices; and increased network management, to allow powered devices to be monitored and controlled remotely.
It is desirable to provide enhanced functionality for the power sourcing units of power over ethernet systems.